Application of NEDO's Core-Analysis System to the Wasabizawa Geothermal Development Field in Northeast Japan

Abstract

Secondary quartz and calcite minerals in cores and cutting samples from the Wasabizawa geothermal field, Akita Prefecture, Japan, were used for the fluid inclusion measurements, homogenization temperature measurement, melting point of ice measurement and Laser Raman analysis. Among homogenization temperatures at each depth in a well, the lowest value of quartz is nearly the same as the formation temperature estimated by temperature logging. On the other hand, homogenization temperatures of calcite are lower than the formation temperature. This is probably resulted from fact that formation temperature in the past was lower than the present temperature. From this, formation temperature in the present time can be easily estimated, applying homogenization temperature measurement of fluid inclusion in quartz from the Wasabizawa field. Moreover, there is a possibility that information about thermal history can be obtained, combining the measured data from some different kinds of minerals. The melting point of ice measurement indicates that salinity of fluid inclusions in quartz from the western part of the field is higher than that from the eastern part. This trend is just similar to that of chloride concentration of geothermal brine.